Experimental and theoretical investigation of fiber-reinforced geopolymer mortars: Mix design optimization and bond behavior with brick masonry

Despite being utilized for thousands of years, masonry structures still face significant challenges in enhancing their integrity and durability, making the preservation of architectural heritage and the development of innovative repair solutions critical. Geopolymer mortar (GM), an environmentally friendly alternative to traditional cement-based materials, shows considerable promise in both new construction and repair of masonry structures. This study systematically investigated the effects of water-binder ratio, binder-sand ratio, water-reducing agent content, and curing age on the setting time, fluidity, compressive strength, and flexural strength of GM. Additionally, the bond strength between GM with different mix ratios and brick masonry was thoroughly examined, along with the bonding performance of fiber-reinforced geopolymer mortar (FRGM) with brick masonry. The findings of this study demonstrated that the water-binder ratio was a crucial factor influencing the workability of GMs. An increase in this ratio significantly prolonged the setting time and improved flowability, while the binder-sand ratio played a secondary role in affecting workability. The mechanical strength of GMs significantly improved by reducing both the water-binder and binder-sand ratios, as well as with prolonged curing. The optimal dosage of a superplasticizer effectively enhanced mortar strength. In addition, the shear bond strength between GM and brick masonry progressively decreased with increasing water-binder and binder-sand ratios. A model for calculating bond strength was proposed, with theoretical values closely aligning with experimental results. The bond strength between FRGM and brick masonry significantly increased with extended bond length, though the rate of increase gradually declined. The bond strength between carbon fiber mesh-reinforced geopolymer mortar and brick masonry was the highest among the three types of fiber meshes. Basalt fiber mesh exhibited a comparable bond strength, and glass fiber mesh exhibited the lowest bond strength. This study provided important experimental and theoretical support for the design and optimization of high-performance GMs in engineering structure application.